The invention is used preferably, though in a non-exclusive manner, in the context of jugs for domestic use, which are widely used to purify and/or filter, for consumption purposes, water taken from the urban mains water network.
Jugs of this type typically comprise a first vessel for collecting the water to be filtered and a second vessel which communicates with the first vessel by a suitable pipe, in which there is accommodated a suitable filter cartridge. The water admitted into the first vessel flows, generally simply by the effect of gravity, through the filter cartridge, thereby flowing into the second vessel, in which it is collected and made available for use. The filter cartridge comprises a chamber, in which filtering material based on activated carbon and/or resin with ionic exchange is contained and through which the water to be filtered is caused to pass in order to fall into the second vessel of the jug.
Since the degree of filtration of the water depends on the time of contact between the water and the filtering material present in the cartridge, it is desirable that the contact time is as constant as possible during the entire phase involving passage from the first vessel to the second vessel of the jug. However, this ideal condition is far from being fulfilled in conventional jugs. The operation for filtering the water is in fact of a discontinuous type, bringing about almost instantaneous pouring of all the water to be filtered in the first vessel and allowing it then to pass by falling into the second vessel.
In that manner, the rate of flow of water through the cartridge (and therefore the time that it spends inside the cartridge) is variable over time, generally being inversely proportional to the height of the column of water present in the first vessel and acting on the filter cartridge. Not only that, the filtered water collected in the second vessel can reach and exceed in terms of height the base of the filter cartridge, bringing about a corresponding counter-pressure which further slows down the passage of the water from the first vessel to the second.
In definitive terms, it is found that the contact time of the water with the filter cartridge is relatively short for the first portion of water which passes from the first vessel to the second and, conversely, is relatively long for the last portion thereof.
In attempting to regularize this phenomenon, there have been provided various technical solutions, one of which provides that the filtered water from the cartridge returns along the pipe in which the cartridge is accommodated and is admitted into the second vessel through a hole which is formed at a location higher than the base of the cartridge, in the vicinity of the first vessel. In that manner, the counter-pressure effect resulting from the water present in the second vessel is at least prevented or limited.
However, the results obtained by known jugs are not satisfactory and the above-described disadvantage is not substantially resolved.